Yes, no one is debating the fact that the climate changes without human intervention. We're just establishing that, at the moment, humans have a huge impact. Even if the total climate change effects within a particular year have a larger component from natural variation than from manmade effects, the anthropogenic components don't tend to fluctuate up and down, they push the climate in a single direction. Nature can do the same thing, but on much greater timescales than what we're seeing from anthropogenic change. We have a good understanding of the processes that can cause global temperature changes, and we know that humans contribute largely to these processes--so why is it so hard to believe that humans are contributing greatly to climate change?